1. Field
The invention is directed toward electronic filters and methods of their use. Specifically, the invention is directed toward reflectionless electronic filters and methods of their use.
2. Background
Virtually all electronic systems use some kind of filtering to reject unwanted frequency components. In most conventional filters, the rejected signals are bounced back to the source, eventually dissipating in the generator itself, or in the interconnecting wires/transmission lines, or being radiated into the instrument housing. This manner of rejecting unwanted signals can sometimes lead to harmful interactions with other components in the system, either by spurious mixing in non-linear devices, unintentional re-biasing of sensitive active components, or cross-talk between various signal paths. A solution was sought for a filter that would absorb these unwanted signals before they could compromise performance. This led to a novel absorptive filter topology which was patented in 2013 (U.S. Pat. No. 8,392,495) as well as pending U.S. patent application Ser. No. 14/724,976 the entirety of both of which are incorporated by reference herein. These absorptive filters solved many problems encountered with conventional filters, such as the sensitivity of mixers to poor out-of-band terminations, detrimental and difficult-to-predict non-linear effects from reactive harmonic loading, leakage or cross-talk due to trapped energy between the filter and other poorly-matched components, and numerous other problems associated with out-of-band impedance matching. They also realized superior performance and manufacturability when compared to other approaches to absorptive filters, such as terminated diplexers and directional filter structures employing quadrature hybrids.
None of these prior embodiments, however, adequately taught how to implement such designs using transmission lines rather than lumped elements. The inability to easily convert these into transmission line form constrained the frequencies at which they could be effectively implemented to the cm-wave range and below. Recent efforts to address this issue have yielded a practical transmission line solution which extends the frequency range easily into submillimeter-waves while maintaining the benefits of the original reflectionless filter topology.